The continuous preparation of food products such as meat balls, chicken breasts, sausage links and patties and the like have been carried out very successfully within a controlled atmosphere contained within in a linear extending oven. Co-inventors Clark K. Benson and Andrew A. Caridis were named in patents which disclosed novel apparatus and processes for heating and cooking foods in a substantially closed treatment chamber, U.S. Pat. Nos. 3,947,241, granted Mar. 30, 1976, 4,167,595, granted Sep. 11, 1979, and 4,949,629, granted Aug. 21, 1990. The treatment chambers disclosed in those patents contain longitudinally extending, endless conveyors which carry the food products through the oven outlets which were displaced a distance from the oven inlets many times by as much as sixty feet thereby requiring on the order of seventy to seventy-five feet of unobstructed floor space in the processing plant where the ovens were installed. In numerous facilities the requisite length of floor space for an elongated oven was difficult to obtain and often plant building extensions were constructed to house the long ovens while in other instances the purchase of a long oven unit was deferred until space could be made available.
The advantages of increasing cooking conveyor length within a housing by including multiple conveyors within an oven are well understood. In some instances conveyors have been arranged in multiple passes with one conveyor flight stacked atop another. Further, the space-saving advantage of arranging the conveyor in a spiral configuration so as to obtain a long cook length in a volume more compact than that in a linear oven is well recognized. Among the problems that arise when configuring the food treatment conveyor in a spiral within a closed box-like housing is how best to promote the even flow of the process vapor with respect to the products carried upon the spiral conveyor belt. Certain workers in the field proposed creating a steady-state, static atmosphere within the oven enclosure while others proposed moving a cooking atmosphere vertically through the open rods or wire mesh in the spiral conveyor stack. Neither of these arrangements satisfies the need for minimizing the pockets of stagnant, slow-moving cooking vapor around the product. Where efficient use is made of the cooking vapor, virtually all of the products on a conveyor belt receive virtually the same heat load and exposure to the cooking vapor, which results in more predictable and uniform products. This is especially true where breaded chicken, meatloaf, shrimp and similar products are treated in a moving cooking atmosphere.
The hot cooking atmosphere applied to a food product may contain, in the case of a direct gas fired oven, the products of combustion including nitrous oxide [NOX] which is believed to cause "pinking" of the inner meat in some poultry products. While the human health risk of pink meat in poultry products is still an open question, food processors have taken the position that such color is to be avoided in cooked chicken parts. Indirect firing or electric heating of the cooking atmosphere in an oven for cooking poultry has been shown to eliminate or to reduce substantially the tendency to produce pink colored but cooked meat. An oven of a design which permits indirect heating by gas firing, electric or thermal fluid heating is very desirable.